1. Field of the Invention
The present invention relates to a display device and a method for producing the same. In particular, the present invention relates to a display device provided with a substrate which has actuator elements, an optical waveguide plate, crosspieces which is interposed between the optical waveguide plate and the substrate and which surround the actuator elements, and picture element assemblies which are joined onto the actuator elements. The present invention also relates to a method for producing the same.
2. Description of the Related Art
Those hitherto known as the display device include, for example, cathode ray tubes (CRT) and liquid crystal display devices.
Those known as the cathode ray tube include, for example, ordinary television receivers and monitor units for computers. Although the cathode ray tube has a bright screen, it consumes a large amount of electric power. Further, the cathode ray tube involves a problem such that the depth of the entire display device is large as compared with the size of the screen.
The liquid crystal display device is advantageous in that the device is thin, and the display device consumes a small amount of electric power. However, the liquid crystal display device involves such problems that it is inferior in brightness or luminance of the screen, and the field angle of the screen is narrow.
In the case of the cathode ray tube and the liquid crystal display device, it is necessary for a color screen to use a number of picture elements (image pixels) which is three times a number of picture elements used in a black-and-white screen. For this reason, other problems also arise such that the device itself is complicated, a great deal of electric power is consumed, and the cost is high.
In view of the above, in order to solve the problems as described above, a new display device 200 has been suggested. As shown in FIG. 20, the display device 200 comprises an actuator substrate 202, an optical waveguide plate 204, and a plurality of crosspieces 206 allowed to be interposed between the actuator substrate 202 and the optical waveguide plate 204. The optical waveguide plate 204 and the crosspieces 206 are joined to one another by the aid of an adhesive 207. The actuator substrate 202 has actuator elements 208 each of which is displaceable toward the actuator substrate 202 or toward the optical waveguide plate 204 at a position surrounded by the plurality of crosspieces 206. A unit dot 212 is constructed by the actuator element 208 and a picture element assembly 210 which is provided on the actuator element 208. The display device 200 is provided with a plurality of unit dots 212.
In the display device 200 described above, the picture element assembly 210 is softened mainly due to the heat generated, for example, by the driving of the actuator element 208, the light 214 introduced into the optical waveguide plate 204, and the driving circuit related to the image display.
Further, the picture element assembly 210 is continuously pressed to make contact with the optical waveguide plate 204 in accordance with the driving of the actuator element 208. As a result, the concave/convex shape or irregular texture on the surface of the picture element assembly 210, which is formed in order to improve the response characteristics of the picture element assembly 210 to make the contact/separation with respect to the optical waveguide plate 204, is progressively changed to be flat.
The adhesion suppressant, which is previously added to the picture element assembly 210 and which remains even after the curing of resin, gradually seeps out from the picture element assembly 210 in association with the contact/separation operation of the picture element assembly 210 with respect to the optical waveguide plate 204. The adhesion suppressant adheres to the optical waveguide plate 204, resulting in the occurrence of the white defect in which the adhered matter glows white.
As a result, the response performance of the contact/separation of the picture element assembly 210 with respect to the optical waveguide plate 204 may be deteriorated, and the picture element assembly 210 may fail to make separation from the optical waveguide plate 204 any longer to cause the change into the bright defect of such a state that the light is always emitted, or the white defect level on the display may be gradually changed to cause any fluctuation in the image display ability.
Problems will now be enumerated in detail below. In order to stabilize the image display, it is necessary that the surface shape of the picture element assembly 210 is not changed. Specifically, it is necessary that the surface shape is not changed in an atmosphere represented by a temperature (heat resistance) of about 60xc2x0 C.
The heat resistance (Tg) of the resin after the curing is low in the present resin system (resin system of the picture element assembly 210). Therefore, it is impossible to suppress the change in shape of the resin due to the heat even when the heating treatment is performed beforehand. As a result, when the driving of the actuator element 208 is continued after the heating treatment, the surface shape of the picture element assembly 210 is gradually changed.
When a resin of the thermosetting type is used as the picture element assembly, the heat resistance (Tg) of the resin is improved, if the heating treatment is performed. Therefore, it is inevitable to perform any heating treatment in the process steps. However, if a resin in an uncured state is directly subjected to the heating treatment, there are some problems.
Firstly, the viscosity of the resin and/or the adhesion suppressant in the picture element assembly precursor is strikingly lowered by the heating. Even when the adhesion suppressant seeps out from the resin due to the incompatibility between the resin and the adhesion suppressant, the mutual leveling is consequently caused without forming any concave/convex structure. As a result, the surface shape of the picture element assembly 210 becomes flat.
Secondary, if an adhesion suppressant, which is prepared to have a high viscosity, is added in order to suppress the leveling, the effect to suppress the adhesion may be lowered. Further, it is difficult to wash out the seeped adhesion suppressant having the high viscosity in the washing step to be performed thereafter. The white defect may be caused on the display.
Finally, the resin may be cured without any sufficient seepage of the adhesion suppressant from the resin, the surface shape of the picture element assembly 210 may become flat, and it is impossible to obtain any sufficient effect to cause the release from the optical waveguide plate 204.
Consequently, a delay may occur in the response of the contact/separation of the picture element assembly 210 with respect to the optical waveguide plate 204, or the state (bright defect), in which no separation takes place, may arise.
It has been revealed that the heat resistance of the resin itself has the greatest influence, as the factor to bring about the change in shape of the resin as described above.
The factor to cause the change in level of the white defect on the display includes the fact that the adhesion suppressant, which has remained in an excessive amount in the picture element assembly 210, seeps out to remain on the optical waveguide plate 204. This phenomenon is caused as follows. A large amount of the adhesion suppressant remains in the picture element assembly 210. When the picture element assembly 210 is pressed to make contact with the optical waveguide plate 204 in accordance with the driving of the actuator element 208, the adhesion suppressant gradually seeps out in such a way that the adhesion suppressant is squeezed out to adhere to the optical waveguide plate 204. As a result, the fluctuation of the white defect level on the display (to gradually become white) is caused.
Further, the adhesion suppressant seeps out to the interface between the picture element assembly 210 and the optical waveguide plate 204, and the adhesive force of the adhesion suppressant with respect to the optical waveguide plate 204 is increased by the heating. It becomes impossible to sufficiently remove the adhesion suppressant by means of any simple washing treatment. The adhered matter, which remains on the optical waveguide plate 204, causes the white defect on the image display.
The present invention has been made taking the foregoing problems into consideration, an object of which is to provide a display device and a method for producing the same in which it is possible to improve the heat resistance of picture element assemblies and it is possible to improve the response performance of the contact/separation with respect to an optical waveguide plate and stabilize the image display.
According to the present invention, there is provided a display device comprising a substrate which has actuator elements, an optical waveguide plate, crosspieces which is interposed between the optical waveguide plate and the substrate and which surround the actuator elements, and picture element assemblies which are joined onto the actuator elements; wherein the picture element assembly includes a layer containing a major component of a cured resin obtained by polymerization with a principal ingredient which is composed of one or more materials selected from modified epoxy, bisphenol A type epoxy, bisphenol F type epoxy, and glycidyl ether type epoxy, and a curing agent which is composed of one or more materials selected from modified polyamine, modified alicyclic polyamine, and heterocyclic diamine modified product of tertiary amine.
The picture element assembly includes the layer containing the major component of the cured resin as described above. Therefore, the heat resistance of the picture element assembly is improved. Accordingly, the response performance of the contact/separation with respect to the optical waveguide plate is improved. Further, the stability of the image display is enhanced.
The picture element assembly may include the layer containing the major component of the cured resin obtained by the polymerization with the principal ingredient which is composed of one or more materials selected from modified epoxy and bisphenol A type epoxy, and the curing agent which is composed of one or more materials selected from modified polyamine and modified alicyclic polyamine, or the layer containing the major component of the cured resin obtained by the polymerization with the principal ingredient which is composed of bisphenol F type epoxy or a mixture of bisphenol F type epoxy and glycidyl ether type epoxy, and the curing agent which is composed of modified polyamine or heterocyclic diamine modified product of tertiary amine.
In the display device constructed as described above, a part of the layer may be opposed to the optical waveguide plate. In this arrangement, the response performance of the contact/separation of the picture element assembly with respect to the optical waveguide plate is improved.
In the display device constructed as described above, when an adhesion suppressant is contained in the cured resin, it is possible to avoid such a phenomenon that the picture element assembly continues the adhesion to the optical waveguide plate. In this arrangement, it is preferable that when a precursor of the cured resin is defined as a resin precursor, the resin precursor and the adhesion suppressant are contained in the layer in a blending rate of 1:0.01 to 1:0.2 as represented by weight ratio.
It is preferable that the adhesion suppressant contains silicone grease and/or silicone oil. In this arrangement, it is preferable that the silicone grease and the silicone oil are contained in a blending rate of 1:0.1 to 0:1 as represented by weight ratio. The silicone grease may contain an inorganic filler.
As for the surface shape of the picture element assembly (especially the shape opposed to the optical waveguide plate), the leveling hardly occurs after the seepage to the interface, when the silicone grease, which is contained in the adhesion suppressant to be added to the resin precursor, has high thixotropy. The picture element assembly keeps the shape of the surface to which the silicone grease seeps to the surface. Therefore, the concave/convex structure or the irregular texture is apt to be formed. The surface shape is formed in such a way that the concave/convex structure is transferred to the surface of the picture element assembly. Accordingly, the response performance of the contact/separation of the picture element assembly with respect to the optical waveguide plate is improved.
As for the silicone oil, the leveling hardly occurs when the viscosity is high. An equivalent effect is obtained such that the more uniform concave/convex structure can be formed suitably over the entire interface between the picture element assembly and the optical waveguide plate. However, the silicone oil is apt to remain as a residual matter on the optical waveguide plate after the washing step to be performed thereafter. Therefore, the viscosity of the silicone oil to be added to the resin precursor may be selected considering the balance between the response performance of the contact/separation depending on the surface shape of the picture element assembly and the degree of occurrence of the white defect on the display due to the residual matter.
When the viscosity of the silicone oil to be added is lowered, the adhesion suppressant, which is subjected to the seepage, tends to undergo aggregation and leveling. As a result, deviation arises in the concave/convex structure of the surface shape of the picture element assembly, and/or the flat portion having no concave/convex structure is increased. Therefore, the response performance of the contact/separation may be lowered.
Therefore, it is preferable that dimethyl silicone oil having a viscosity of 5 mm2/s to 3000 mm2/s is used as the silicone oil described above. In this arrangement, the adhesion-suppressive effect is improved, it is easy to remove the adhesion suppressant adhered to the optical waveguide plate in the washing step, and it is possible to suppress the occurrence of the white defect on the display.
When an anti-foaming agent is contained in the cured resin, then the picture element assembly is prevented from contamination with bubbles, and it is possible to suppress the generation of any unnecessary scattered light.
According to another aspect of the present invention, there is provided a method for producing a display device comprising a substrate which has actuator elements, an optical waveguide plate, crosspieces which is interposed between the optical waveguide plate and the substrate and which surround the actuator elements, and picture element assemblies which are joined onto the actuator elements; the method comprising a step of preparing a picture element assembly precursor containing a mixture composed of one or more principal ingredients selected from modified epoxy, bisphenol A type epoxy, bisphenol F type epoxy, and glycidyl ether type epoxy, and one or more curing agents selected from modified polyamine, modified alicyclic polyamine, and heterocyclic diamine modified product of tertiary amine; a step of patterning the picture element assembly precursor; a step of joining the optical waveguide plate and the substrate; and a step of curing the picture element assembly precursor to form the picture element assembly.
In this process, the picture element assembly is manufactured by curing the picture element assembly precursor obtained by mixing the principal ingredient and the curing agent. Therefore, the heat resistance of the picture element assembly is improved. Accordingly, the response performance of the contact/separation with respect to the optical waveguide plate is improved. Further, the stability of the image display is enhanced.
The step of preparing the picture element assembly precursor may be performed to prepare the picture element assembly precursor containing the mixture composed of one or more principal ingredients selected from modified epoxy and bisphenol A type epoxy, and one or more curing agents selected from modified polyamine and modified alicyclic polyamine, or the picture element assembly precursor containing the mixture composed of the principal ingredient of bisphenol F type epoxy or a mixture of bisphenol F type epoxy and glycidyl ether type epoxy, and the curing agent of modified polyamine or heterocyclic diamine modified product of tertiary amine.
The production method described above may further comprise a step of preheating the picture element assembly precursor prior to the step of curing the picture element assembly precursor. The preheating step makes it possible to adjust the curing level of the picture element assembly precursor. The shape of the picture element assembly precursor can be controlled to be the shape with which the separation is easily made with respect to the optical waveguide plate, at the stage at which the optical waveguide plate and the substrate are joined to one another. Therefore, it is possible to improve the response performance of the contact/separation of the picture element assembly with respect to the optical waveguide plate.
In the production method described above, the step of curing the picture element assembly precursor may include a step of curing the picture element assembly precursor at room temperature, and a step of heating and curing the picture element assembly precursor at a temperature higher than the room temperature.
In this process, the step of curing the picture element assembly precursor at the room temperature and the step of heating and curing the picture element assembly precursor may be performed while displacing or driving the actuator elements by applying a voltage to the actuator elements.
In the present invention, the picture element assembly precursor may contain an adhesion suppressant, and the method may further comprise a step of allowing the adhesion suppressant to seep out. In this process, the step of allowing the adhesion suppressant to seep out may be performed by applying at least heat and/or vibration. When the method based on the heating is selected for the step of allowing the adhesion suppressant to seep out, the step of allowing the adhesion suppressant to seep out may also serve as the step of preheating the picture element assembly precursor described above.
The step of allowing the adhesion suppressant to seep out may be performed after the step of patterning the picture element assembly precursor, and/or after the step of joining the optical waveguide plate and the substrate, and/or during the step of curing the picture element assembly precursor. The phrase xe2x80x9cduring the step of curing the picture element assembly precursorxe2x80x9d herein means xe2x80x9cduring the step of curing the picture element assembly precursor at the room temperaturexe2x80x9d, xe2x80x9cduring the step of heating and curing the picture element assembly precursorxe2x80x9d, or xe2x80x9cbetween the step of curing the picture element assembly precursor at the room temperature and the step of heating and curing the picture element assembly precursorxe2x80x9d.
The workpiece (in a state before being completed as the display device) may be introduced into the step of heating and curing the picture element assembly precursor without washing the adhesion suppressant which seeps out from the picture element assembly precursor.
The method for producing the display device may further comprise a step of washing the adhesion suppressant which seeps out from the picture element assembly. In this procedure, a pretreatment for the washing step is preferably performed such that the workpiece is immersed in a highly volatile liquid and the actuator elements are driven. Further, the washing step may be performed while displacing the actuator elements by applying a voltage to the actuator elements.
A procedure of the production method of the present invention will be explained below specifically. At first, the step of allowing the adhesion suppressant to seep out is performed at an arbitrary timing in an arbitrary number of times after the step of patterning the picture element assembly precursor, and/or after the step of joining the optical waveguide plate and the substrate, and/or during the step of curing the picture element assembly precursor.
As for a specified procedure for the seepage step, the heat or the vibration is applied (for example, the vibration is externally applied, or the vibration is applied by driving the actuator elements). Accordingly, the adhesion suppressant, which is dispersed in the picture element assembly precursor, tends to seep out by chance to facilitate the seepage.
The picture element assembly precursor is heated and cured at a temperature higher than the room temperature, for example, while allowing the adhesion suppressant to be interposed at the interface between the picture element assembly and the optical waveguide plate, after the step of curing the picture element assembly precursor at the room temperature. When the primary curing is completed in the curing step at the room temperature, it is possible to suppress the sudden softening and the leveling of the resin and the adhesion suppressant during the heating treatment to be performed thereafter.
The adhesion suppressant, which has seeped out to the interface between the picture element assembly precursor and the optical waveguide plate until the curing step at the room temperature, is allowed to remain as it is during the heating treatment, with which the adhesion suppressant, which seeps out by the heating treatment, is combined. Accordingly, it is possible to obtain, after the heating treatment as well, the concave/convex shape equivalent to the concave/convex shape of the surface of the picture element assembly precursor obtained upon the curing at the room temperature.
When the series of heating treatments are performed as described above, then the separation is facilitated for the resin and the adhesion suppressant as compared with a case in which only the curing step at the room temperature is performed, and the amount of the adhesion suppressant remaining in the resin is decreased. Therefore, when the actuator elements are driven thereafter, it is possible to decrease the amount of the adhesion suppressant which seeps out from the picture element assemblies by the contact/separation of the picture element assemblies with respect to the optical waveguide plate, and it is possible to suppress the fluctuation of the white defect level on the display.
Further, the following subsidiary effect is also obtained. It is possible to decrease the amount of addition of the adhesion suppressant itself to be added to the picture element assembly precursor, which is advantageous in view of the cost as well.
In the pretreatment for the washing step, the entire workpiece is immersed in the highly volatile liquid, and the actuator elements are driven in the immersion liquid. Accordingly, the adhesion suppressant having the high viscosity, which has seeped out to the interface between the optical waveguide plate and the picture element assemblies, is forcibly mixed with the highly volatile liquid having the low viscosity. When the highly volatile liquid is poured into the gap between the optical waveguide plate and the substrate to perform the washing thereafter, it is easy to remove the adhesion suppressant.
Further, when the step of once separating the picture element assemblies from the optical waveguide plate by previously applying a high voltage to the actuator elements is added before effecting the driving of the actuator elements in the immersion liquid, then it is possible to reliably perform the washing for the normal picture element assemblies, and it is possible to effectively suppress the occurrence of the white defect on the display.
Also in the washing step to be performed thereafter, the washing effect is also improved by performing the washing in the state in which the voltage is applied to the actuator elements to cause the displacement, i.e., in the state in which the gap is given between the picture element assemblies and the optical waveguide plate. Accordingly, it is possible to reliably remove the adhesion suppressant which would be otherwise hardly removed as a result of the heating. Thus, it is possible to suppress the occurrence of the white defect on the display.
After the washing step described above, the adhesion suppressant may be lost due to the washing treatment. If this state is maintained, the release performance may be deteriorated at the interface between the picture element assembly and the optical waveguide plate, resulting in the decrease in response characteristics of the contact/separation of the picture element assembly with respect to the optical waveguide plate, or resulting in the occurrence of the luminance deficiency.
In view of the above, when the adhesion suppressant is poured into the space between the picture element assemblies and the optical waveguide plate after the washing step, it is possible to recover the release performance at the interface between the picture element assemblies and the optical waveguide plate. It is possible to avoid the occurrence of the luminance deficiency and the decrease in the response characteristics of the contact/separation of the picture element assembly with respect to the optical waveguide plate as described above. It is preferable to use silicone oil as the adhesion suppressant in order to recover the release performance at the interface between the picture element assembly and the optical waveguide plate.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.